Kevin C. O'Brien

Relationship between gas separation properties and chemical structure in a series of aromatic polyimides

Abstract Gas permeabilities and permselectivities for various gas pairs [He/CH 4 , CO 2 /CH 4 , N 2 /CH 4 , and O 2 /N 2 ] are reported for a series of aromatic polyimides synthesized in our laboratory. Gas solubility and diffusivity data are also reported for some of the polyimides. Systematic variations in chemical structure were found to lead to significant changes in permeabilities and selectivities. Further analysis shows that the permeability and selectivity changes in these cases are primarily due to the alteration of diffusivity factors. Generally, increases in permeability are attended by losses in permselectivity; however, some of the polyimides in the present series of materials were found to deviate very favorably from this typical behavior. Specifically, materials were discovered having simultaneously higher permeabilities and permselectivities than commercial polymers currently being used as membrane materials. The relationship between gas separation properties and chemical structure is discussed in terms of intrasegmental mobility and intersegmental packing of the constituent polymers. The experimental data and their physical implications suggest the possibility that many new polymers having both high permeability and selectivity can be designed by tailoring the intrasegmental mobility and intersegmental packing of membrane polymers.

A new technique for the measurement of multicomponent gas transport through polymeric films

Abstract An apparatus to measure mixed gas permeation through polymer films is described. The system, based on a combination of manometric and gas chromatography techniques, allows straightforward determination of film permeabilities and selectivities over a wide range of feed pressures and compositions. This approach eliminates the need to use a downstream sweep gas and can be implemented by simple modification of pure gas permeation cells. Pure and mixed gas permeation data in polycarhonate films are reported for carbon dioxide and methane to illustrate the use of the equipment. The deviations between the pure and mixed gas results tend to be small and can he explained in terms of current theories of gas transport in glassy polymers.

Polyimide materials based on pyromellitic dianhydride for the separation of carbon dioxide and methane gas mixtures

Abstract The sorption and transport of carbon dioxide and methane in a series of dense polyimide films were examined to evaluate these materials for gas separation applications. The polyimides described in this study are based on the reaction of pyromellitic dianhydride (PMDA) with oxydianiline (ODA), methylene dianiline (MDA), or isopropylidene dianiline (IPDA). The carbon dioxide permeabilities for this series of compounds increased in the order: PMDA-ODA

Polymerization of 16-heptadecenoic acid monolayers ☆

Abstract Monolayers of heptadecenoic acid (vinyl acid) were spread at a gas-water interface. The terminal double bond of the vinyl acid enabled it to be polymerized on exposure to UV radiation. Pressure-area isotherms for both monomer and polymer vinyl acid were then recorded and compared with isotherms from similar compounds. Preliminary studies were conducted to minimize the degree of dissolution of the fatty acid. The polymerization kinetics were examined by the use of UV spectroscopy and measurements of the reduction in the area occupied by the film at a constant surface pressure. The reaction appeared to follow zero-order kinetics after an initial acceleration period. The rate constant for the reaction increased with increasing surface pressure. A dynamic mechanical test was performed to determine the mechanical properties of monolayers at the gas-water interface. Films were polymerized to various conversions and then examined to determine the relation between mechanical properties and conversion. A simple model is proposed to correlate the monolayers structure and the dynamic mechanical data.